Pelletized immobilized amine sorbent for CO2 capture

ABSTRACT

The disclosure describes a pelletized sorbent comprising a first component comprising Basic Immobilized Amine Sorbent, a second component comprising inorganic strength additive, and a third component comprising polymer binder, where the Basic Immobilized Amine Sorbent and solid inorganic strength additive are interconnected by the polymer binder. The pelletized sorbent is useful for removing CO2 from a gaseous mixture such as a post combustion gas stream.

RELATION TO OTHER APPLICATIONS

This patent application is a continuation-in-part of and claims priorityfrom nonprovisional patent application Ser. No. 15/156,773 filed May 17,2016, which issued as U.S. Pat. No. 10,065,174 and claims the benefit ofprovisional application 62/233,493 filed Sep. 28, 2015, which are herebyincorporated by reference.

GOVERNMENT INTEREST

The United States Government has rights in this invention pursuant tothe employer-employee relationship of the Government to the inventors asU.S. Department of Energy employees and site-support contractors at theNational Energy Technology Laboratory.

FIELD OF THE INVENTION

The disclosure provides a pelletized sorbent for removal of carbondioxide from a gaseous mixture. The pelletized sorbents are comprised ofBasic Immobilized Amine Sorbent in particle or pellet form, inorganicstrength additive, and a polymer binder.

BACKGROUND OF THE INVENTION

Carbon sequestration is a viable alternative to reducing the emissionsof the greenhouse gas carbon dioxide (CO₂) from large point sources. Itholds the potential to provide deep reductions in greenhouse gasemissions. Carbon sequestration is a two-step process where the captureof carbon dioxide from a gas stream is followed by permanent storage.The capture step for carbon dioxide represents a major cost in theoverall process.

Of particular interest are power generation point sources that usefossil fuels. Since nearly one-third of the anthropogenic CO₂ emissionsare produced by these facilities, conventional coal-burning power plantsand advanced power generation plants—such as integrated gasificationcombined cycle—present opportunities where carbon can be removed andthen permanently stored. At the current time, pulverized coal-fired-basesteam cycles have been the predominant electric power generationtechnology. These will continue to be used predominantly in the nearfuture. Technologies for capturing CO₂ will need to be applied to newmore efficient coal-fired facilities and will need to be retrofittedonto existing plants.

For coal-fired power plants, the conventional scrubbing system that iscurrently the comparative baseline for all other capture technologies ismonoethanolamine (MEA) scrubbing. This wet scrubbing process removes theCO₂ in an absorber and then regenerates the spent scrubbing liquor in avessel by indirectly heating the solution with plant steam. Althoughthere have been large scale commercial demonstrations of thistechnology, the process has several disadvantages, such as a high heatof reaction, low working capacity, corrosiveness of the solution, thesusceptibility of being poisoned, and most notably, its need to be in anaqueous solution. This latter disadvantage results in a large energyneed to regenerate the spent solution, especially the sensible heatingof the water, which is a minimum of 70 wt % of the solution. The wateris recognized as an inert carrier between the absorption andregeneration steps. Another energy loss while regenerating the spent MEAsolution includes evaporative heat loss of vaporizing liquid water.

One type of novel CO₂ capture technology that can be applied to variousgas streams has, as a basis, dry regenerable solid sorbents. Examples ofthese types of sorbents are zeolites, activated carbon, alkali/alkalineearth metals, immobilized amines, metal organic framework, etc. Aspecific sorbent category that shows significant advancement areamine-based solid sorbents, such as Basic Immobilized Amine Sorbents(hereinafter BIAS). BIAS consist of amines (primary, secondary,tertiary, or a combination thereof) deposited onto a porous support. Themanner of deposition can be random or structured deposition of the amineonto this support (silica, polymer, etc.). When used in the industrialsetting, the dry solid sorbent process may act in a similar fashion tothe wet scrubbing process in that the sorbent would be transportedbetween an adsorption step and a regeneration step and in that thesorbent is regenerated by a temperature-swing application.

One of the main benefits in using the solid sorbent is the eliminationof the sensible heat for the liquid water as compared to MEA. Asecondary benefit lies in the lower heat capacity for the solid versusthe liquid solvent, also serving to lower the sensible heat required.More CO₂ can be adsorbed on a weight or volume basis with theamine-based solid sorbents, so the sorbent system is capable of asignificant decrease in the heat duty for the regeneration step. A lowercost of energy service for process involving BIAS as compared to aminewet scrubbing may also result. Thus amine-based solid sorbents have thecapability to improve the overall energetics of CO₂ capture.

Effective amine-based solid sorbent methodologies are needed for carbondioxide capture from a gaseous mixture, whether the capture occurs incombustion or gasification power generation systems from flue gas, or inother applications such as natural gas sweetening. Because of the highconcentration of carbon dioxide in any of these feed streams, a largequantity of the gas will be reacting with the sorbent and thus produceconsiderable amounts of exothermic heat. This heat must be removed fromthe sorbent to prevent temperature instability within the reactor, toassure the sorbent will operate at optimum temperature, and to eliminatethe potential degradation of the sorbent because of high temperatureexcursions.

Unfortunately, reactor designs which are amenable to flowing solidsorbents present issues with management of those mobile solid sorbent.For example, sorbents of a particle size capable of efficient CO₂adsorption are often easily aerosolized, carried into a flue stream, andprogressed further through the reactor system where they cause damage todownstream components and are overall lost. Sorbent particles ofsufficient size not to be at risk for being aerosolized aresignificantly less efficient at sorption per unit mass, which leads toan increase in the mass of sorbent required. Further, sorbent particlesthemselves are vulnerable in industrial processes as they do not havethe structural integrity necessary for prolonged use in reactors. Wherethe sorbent has low structural integrity and readily breaks down,greater material investment is required and the sorbent becomes lesseconomical to utilize over other competing materials and methods.

Basic Immobilized Amine Sorbents (BIAS or sorbents) and their associatedprocesses are among the most widely studied solid sorbents to mitigatepost-combustion carbon dioxide (CO₂) emissions. BIAS are organized intothree classes (1-3) according to their preparation procedure and amineimmobilization mechanisms. Class 1 sorbents are generally prepared bydry or wet impregnation of a support, namely different grades of silica,with a polyamine/hydrophilic solvent (methanol, ethanol, etc.) mixture.Principal polyamines employed are tetraethylenepentamine (TEPA),polyethylenimine (PEI), and generally various linear or branchedpolyamines that possess different ratios of —NH₂ (primary)/—NH(secondary)/—N (tertiary) amine groups that can potentially adsorb CO₂.These polyamines are bound to the supports by Si—OH—NH₂ hydrogen bondingand also ionic SiO⁻. . . —NH₂ ⁺/—NH⁻ interactions. Primary and secondaryamines can capture CO₂ under dry and wet conditions while tertiaryamines primarily capture CO₂ only under humid conditions. The manner ofamine deposition to the support can be random or structured depositionof the amine onto the support. In addition to silica, other supports mayinclude clays, polymers, activated carbons, zeolites, and others.

Class 2 sorbents are typically prepared by wet impregnation of a mixtureof a reactive aminosilane and anhydrous hydrophobic solvent, usuallytoluene, onto a dry, pre-treated silica support. Strict control of theH₂O content within the system is maintained to manipulate the subsequentgrafting reaction between the aminosilane and the silica support. Thegrafted aminosilanes are immobilized to the silica support via covalentSi—O—Si linkages. These Si—O—Si linkages are also responsible forimmobilizing the aminosilane within the bulk of the pore viapolymerization.

BIAS sorption capacity is typically calculated either on aweight-percent-of-sorbent basis or mmol CO₂/g-sorbent basis. For weightpercent basis, the weight of adsorbed CO₂ is divided by the weight ofsorbent and multiplied by 100. For the mmol CO₂/g-sorbent basis, theweight of adsorbed CO₂ is divided by the molecular weight of CO₂ (44g/g-mole), multiplied by 1,000, and divided by the sorbent weight. Thesorption capacity of a pelletized sorbent is best measured by exposingthe pellet to a CO₂ concentration of ppm level to 100% CO₂ at 0 to 120°C. for a period of time until the maximum amount of CO₂ is adsorbed bythe sorbent, usually less than or equal to 1 hour. Preferentialdetermination of pellet CO₂ capture capacity involves placing the pelletin a thermogravimetric analyzer (TGA) or fixed bed reactor and exposingthe pellet to 10-15 vol % of flowing CO₂ with a balance of either air orinert He or N₂ at 40-75° C. The CO₂ concentration range and adsorptiontemperature here are either in the range of coal-fired power plant fluegas, or can be achieved with minimal process modification. The pellet isfirst heated at 100-110° C. for 10-60 min under flowing air or an inertgas to remove any pre-adsorbed water or CO₂ (from the environment). Todetermine the CO₂ capture capacity of the pellet in the case of the TGAsystem, the final weight of the sorbent after CO₂ adsorption issubtracted from the initial weight of the sorbent after pre-treatment,and the weight difference is used to calculate the CO₂ capture capacity.In the case of the fixed bed, CO₂ gas concentration profiles from aneffluent measuring device, such as a mass spectrometer, are analyzed andused to calculate the CO₂ capture capacity of the pellet.

Advancements in reactor design from batch, fixed-bed systems tocontinuous circulating fluidized bed, rotating disk, and moving bedsystems, and development of a steam-stable sorbent under practicalconditions are promising milestones towards commercialization. However,the aforementioned inherent difficulties in the application of such asmall particle-size sorbent to industry scale processes remain. Forexample, BIAS degrades structurally over time as the material is movedfrom one industrial environment to another. Additionally, the light BIAScan be picked up by and carried into a gas stream, leading to loss ofthe material and degradation of components downstream. Further, thecurrent amine based sorbent technology utilized in CO₂ separation isthat the impregnated liquid amines of the BIAS sorbents are vulnerableto leaching from the sorbent pores by condensed steam during practicalCO₂ adsorption-desorption testing under humidified conditions. Thedeleterious effect of steam on the CO₂ capture of BIAS materials iswidely seen in the literature, and was attributed to, in part, amineleaching from the sorbents. Additional difficulties with small particlesorbents include high energy costs to overcome large pressure dropacross sorbent beds and failure of, specifically, internal moving parts(valves, conveyors, etc.) by agglomerated or aerosolized particles.Because of these issues, pelletization of immobilized amine sorbents isadvantageous for their large scale application. It would be advantageousto provide a pelletized sorbent for CO₂ capture using an amine-basedsolid sorbent, where the pelletized sorbent is capable of efficient CO₂sorption while maintaining an appropriate mass and structural integrityfor use in a post-combustion separation system. Such a pelletizedsorbent would achieve acceptable CO₂ adsorption while being of anoptimized volume and mass for incorporation of large loads of thesorbent into a post-combustion reactor system. Additionally, thepelletized sorbent would more easily provide for integration withexisting power or fuel production facilities than current solidsorbents. Thus, through utilization of the pelletized sorbent, increasesin CO₂ capture capability while minimizing energy and infrastructurerequirements is realized.

Accordingly, it is an object of this disclosure to provide a pelletizedsorbent for CO₂ capture comprising: a Basic Immobilized Amine Sorbent,an inorganic strength additive, and a polymer binder.

These and other objects, aspects, and advantages of the presentdisclosure will become better understood with reference to theaccompanying description and claims.

SUMMARY OF THE INVENTION

The disclosure describes a pelletized sorbent comprising a BasicImmobilized Amine Sorbent particle, an inorganic strength additive, anda polymer binder. The pelletized sorbent is useful for removing CO₂ froma gaseous mixture such as a post combustion gas stream.

As illustrated in FIG. 1, the pelletized sorbent comprises at least thethree components Basic Immobilized Amine Sorbent particle, an inorganicstrength additive depicted (as fly ash (FA)), and a polymer binder. Thepolymer binder interconnects the Basic Immobilized Amine Sorbentparticles and inorganic strength additive to form an agglomerated pelletcapable of CO₂ sorption. The interconnection is a result of bothphysical binding of the constituents as well as chemical bonding of thepolymer binder to the Basic Immobilized Amine Sorbent and inorganicstrength additive, thus providing added strength to the pelletizedsorbent. The pelletized sorbent features high crush strength, highattrition resistance, good CO₂ capture, and hydrophobicity for use ingas separation operations.

The pelletized sorbents may remove CO₂ from a gaseous mixture where thegaseous mixture necessarily comprises either pure CO₂ or a mixture ofCO₂ and at least one other gas. An exemplary gaseous mixture is apost-combustion gas stream from power generation. Such a flue gas streamwould comprise N₂ and CO₂ as its primary constituents. Removal inanother exemplary gaseous mixture is the sweetening of raw natural gas,where a stream of raw piped gas primarily comprising primarily NH₄,varying amounts of other hydrocarbons, and CO₂ is sweetened by removalof the CO, such removal accomplished by the pelletized sorbent.

The pelletized sorbents separate CO₂ from the gaseous mixture bysorption of the CO₂. The pelletized sorbents primarily absorb the CO₂ byfirst external diffusion of CO₂ from the bulk gas stream to the surfaceof the pellet; followed by diffusion of CO₂ into the bulk pelletstructure; then pore diffusion into the BIAS particles comprising thepellet; and subsequent reaction of CO₂ with BIAS amine groups. Reactionof CO₂ with the amines will primarily form ammonium-carbamate ion pairs,and potentially carbamic acid and bicarbonate (in the presence of H₂O).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Illustrates the internal structure of a pelletized sorbent.

FIG. 2. Illustrates the effect of fly ash content on the (a) mechanicalcrush strengths and (b) CO₂ capture capacities of pelletized sorbent.

FIG. 3: Illustrates the pelletized sorbent (a) structure and (b)H-bonding mechanisms.

FIG. 4 Illustrates use of (a) a cross-linker and (b) the structure ofcross-linked material using a diamine for poly (vinyl chloride) (PVC)and a dialdehyde for poly(vinyl alcohol) (PVA).

FIG. 5: Illustrates an exemplary preparation procedure of a pelletizedsorbent comprising BIAS/fly-ash/PVC.

FIG. 6. Illustrates IR absorbance intensity profiles for (a) —NH₂ ⁺ and(b) —NH₃ ⁺ species generated during in situ degradation at 105° C. underN₂ flow for FA/EI₄₂₃ (20/80) based pelletized sorbents having PVC₆₂ andPPD-PVC₆₂ binders.

FIG. 7. Illustrates an exemplary preparation procedure for pelletizedsorbents comprising BIAS/fly-ash/PC.

FIG. 8: Illustrates the cyclic CO₂ capture capacities of a pelletizedsorbent comprising EI₄₂₃/fly-ash/PC.

FIG. 9. Illustrates CO₂ adsorption of a pelletized sorbent comprising12.2 wt % PC prepared from binder solutions having different mixingtimes and of the fresh particle E100/S sorbent.

FIG. 10. Illustrates the cyclic CO₂ capture capacities of a pelletizedsorbent comprising E100-S/fly-ash/PC.

FIG. 11. Illustrates the effect of different polymer binders on the CO₂capture capacity and structural integrity.

FIG. 12. Illustrates the CO₂ capture capacity of a PEI/E3/SIO₂ sorbent.

FIG. 13. Illustrates a strategy for pelletized sorbent synthesis.

FIG. 14. Illustrates a comparison of CO₂ capture capacity plus PCR andOCR values of pellets with different ratios of E3/amine (E100 or PEI).

FIG. 15. Illustrates a comparison of PCR value with increasingantioxidant content.

DETAILED DESCRIPTION OF THE INVENTION

The following description is provided to enable any person skilled inthe art to use the invention and sets forth the best mode contemplatedby the inventor for carrying out the invention. Various modifications,however, will remain readily apparent to those skilled in the art, sincethe principles of the present invention are defined herein specificallyto provide a pelletized sorbent for CO₂ capture comprising BasicImmobilized Amine Sorbent particles, an inorganic strength additive, andpolymer binder.

The pelletized sorbent is an agglomeration of the constituent materialscomprising at least Basic Immobilized Amine Sorbent particles, aninorganic strength additive, and polymer binder. The pelletized sorbentmay further compromise additives such as amines, dispersants, andnon-ionic surfactants or other like materials to enhance structuralintegrity or CO₂ migration throughout the pellet. Preferred BIAS forpelletization include Class 1, Class 2, or hybrid class 1/class 2sorbent (as also known as Class 4) types. Preferred sorbents have silicaas the support and amine species that possess any combination of primaryand secondary amines, and tertiary amines. BIAS may also include anepoxy-based chemical cross-linker which covalently joins the aminestogether to enhance their thermal and H₂O stability. Further, BIAS willinclude an inorganic antioxidant, such as NaCO₃ or K₂CO₃, or organicantioxidant as in phenylenediamine, which serves to inhibit amineoxidation. These sorbents are all capable of being pelletized using thecombination of inorganic strength additives and polymer binder asdisclosed herein.

Chemical characteristics of BIAS supports such as silica and zeolitepromote binding of sorbent pellet constituents. For example, the Si—OHgroups of amine/silica supported sorbents and Al—OH groups ofamine/zeolite sorbents interact chemically with aromatic benzene. Thesearomatic groups are present on polymer binders such as polystyrene, withthe resulting polymer-BIAS interactions serving to increase themechanical and structural integrity of the final pelletized sorbents.

Preferred porous supports of the BIAS is any grade of silica with anamorphous, crystalline, or combination of amorphous and crystallinestructure. Preferred types and structures of silica includeprecipitated, fumed, gel, SBA-15, and those with ordered mesoporousstructures such as MCM-41. Preferred physical properties of the BIASsilica support include a surface area (BET) between 0 and 2,000 m²/g,and a pore volume (BJH) between 0 and 5 cm³/g.

Preferred amines for the BIAS are polyamines that contain more than oneas well as any combination of the following amine groups: primary(—NH₂), secondary (—NH), and tertiary (—N) amines. These polyaminescould be nearly pure single components or a combination of differentpolyamines. Examples of some polyamines used in the BIAS include thefollowing: ethylenimine oligomer mixture (EI₄₂₃, linear/branchedmixture, —N/—NH/—NH₂ ratio of 1.3:1:2.2), polyethylenimine withmolecular weights between 400 and 20,000 (PEI, —N/—NH/—NH₂ ratio of1.3:1:1.7 for PEI₈₀₀), E100 (linear, cyclic, branched mixture),tetraethylenepentamine (TEPA, linear, —N/—NH/—NH₂ ratio of 0:1:0.7),pentaethylenehexamine, and hexaethyleneheptamine. Furthermore, theseexamples of amines and other potential amines should have but are notlimited to a molecular weight (MW) range between 180 and 20,000 g/g-moleto avoid excessive loss from the BIAS at CO₂ desorption temperatures(100 to 110° C.) (lower MW values) and to minimize CO₂ diffusionlimitations (higher MW values). Preferentially, BIAS sorbents maypossess an amine loading between 1 and 65 wt %. Preferred BIAS sorbentspossess an amine loading between 20 and 45 wt %. More preferred BIASsorbents possess an amine loading between 45 and 65 wt %.

BIAS may be functionalized for CO₂ sorption either prior to, or after,palletization. Example 1, for example, provides a method forpalletization using BIAS particles requiring only grinding to thedesired size for final pellet formation. In Examples 7 and 8, BIAS isfunctionalized by amine impregnation after pelletization. Accordingly,BIAS includes unfunctionalized BIAS particles during pellet formation.

Chemically cross-linking polymeric amines further increases theirmolecular weight, increases their viscosity, and generally reduces theirH₂O solubility, all of which enhance the H₂O stability of theirassociated immobilized amine sorbents. A key feature herein is thecombination of an N—N-diglycidyl-4-glycidyloxyaniline (E3) tri-epoxide(3 epoxide groups per molecule) cross-linker with higher molecularweight polymer amine species (>400 g/g-mol) containing primarilybranched structures, or branched structures mixed with aliphatic andaromatic. Higher molecular weight branched structures, namepolyethylenimine (PEI₈₀₀), give greater H₂O-stability than lowermolecular aliphatic species for immobilized amine sorbents due to theirhigher viscosity which is partially attributed to the physicalentanglement of the polymer chains and dense hydrogen bonding amonglarge branched chains.

The combination of branched polyethylenimine with the branchedN—N-diglycidyl-4-glycidyloxyaniline was shown to produce a highly porousand H₂O-insoluble polymer network upon the reaction of these species ina porogen at 105° C. after 3 hours. A porous network was also formedwhen the E3 linker was mixed with aliphatic tetraethylenepentamine(TEPA). A porous network was not obtained when the E3 tri-epoxide linkerwas substituted with bisphenol A-based D.E.R 332 di-epoxide (2 epoxidegroups per molecule), and mixed with either TEPA or PEI₈₀₀. Thesuperiority of the E3 linker over the bisphenol A is due to (i) fasterreaction kinetics imparted by the higher concentration of epoxide groupson the E3 tri-epoxide molecule compared to Bisphenol A-based epoxides;(ii) more effective reactions for E3 than for bisphenol A-based linkerswith amines due to more easily and more quickly accessed epoxide groupsof the smaller and lighter E3 cross-linker compared to the bulkier andheavier bisphenol A-based linkers; (iii) better thermodynamiccompatibility of the E3 linker than bisphenol A-based linkers withamines facilitated, in part, by less aromatic groups on the E3 moleculeand the tertiary amine group (nitrogen atom bonded to three functionalgroups and containing no hydrogen atoms) on the E3 molecule; (iv)ability of the E3 linker to capture CO₂ under humid conditions via thetertiary amine group, which is widely known to capture CO₂ in thepresence of water vapor. The combination of a bisphenol A-baseddi-epoxide (EPON) and aliphatic TEPA were used elsewhere in animmobilized amine sorbent. A mono-epoxide, 1,2-epoxybutane, was alsoused in combination with PEI to make other immobilized amine sorbents.The reasons herein described prove a novel and superior application ofthe combination of a branched tri-epoxide with a branched polymericamine or with a mixture of branched polymeric amine/aliphaticamine/cyclic amine for an immobilized amine sorbent. This novelcombination described herein was proven to increase the H₂O stability ofimmobilized amine sorbents in both particle and pellet form. Othertri-epoxide species, like commercially available Heloxy 48 (aliphatictriglycidyl ether-based; Trimethyol Propane Triglycidyl Ether-based) andalso tetra-epoxide species like 4,4′-methylenebis(N,N-diglycidylaniline)may be used. Preferentially, BIAS sorbents contain between 0.01 and 50wt % epoxy-based cross-linker. To give both the amine species and thepolymer binder resistance to oxidative degradation, antioxidants areincorporated into the BIAS pellet formulation. Antioxidants serve, inplace of the amines, as sacrificial electron donors or as electronacceptors towards oxygen radicals. The combination of polymer amines,such as polyethylenimine, with antioxidants, preferably K₂CO₃, has adistinct advantage over a similar combination of aliphaticamine/antioxidant. Whereby, greater oxygen diffusion limitations areimparted to the sorbent by branched PEI's relatively high viscosity thanby the relatively low viscosity of a linear amine. These diffusionlimitations slow the rate of oxygen transport into and oxygenconcentration within the sorbent pores, resulting in slower reactionkinetics with the antioxidant. The solubility of the Group 1 carbonatesin water at 10-20° C. follow as: 1.4 g/100 mL, Li₂CO₃<16.4 g/100 mL,Na₂CO₃<112 g/100 ml, K₂CO₃<260.5 g/100 mL, Cs₂CO₃. Higher solubility ofcarbonates in water lends to a higher ratio of MeOH/H₂O that can be usedin the impregnation solution, resulting in lower solvent evaporationenergy costs for particle sorbents and pellets. Preferred concentrationsof antioxidant in BIAS sorbents is between 0.01 and 10 wt %.

An extension of the pellet impregnation solution containing polyamine,epoxide linkers, and or K₂CO₃ antioxidant is towards a pellet coating.The coating solution would contain any of the herein describedpolyamines, polyepoxides, and antioxidants in any weight ratio relativeto each other component of the solution, with a total concentration insolvent between 0.001 wt % and 99.99 wt %. The solvent could be anysingle liquid or combination of these polar and nonpolar liquids: water,methanol, ethanol, propanol, ethylacetate, diethyl ether, toluene,benzene, dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP),tetrahydrofuran (THF), dioxanes, acetonitrile, chloroform, hexane,dichloromethane, and others. The coating would be applied by suspendingthe amine (plus other components)-functionalized pellet sorbent in thecoating solution and removing the solvent in the rotary-evaporatorset-up. This would deposit a coating of the non-volatile materials onthe pellets outer surface and provide added water resistance/amine leachresistance.

The BIAS in the pelletized sorbent are the primary constituentsresponsible for the CO₂ capture of the pelletized sorbents. PreferredCO₂ capture capacity of the starting BIAS particles before pelletizationis from about 0.1 to about 1.0 mmol CO₂/g. More preferred CO₂ capturecapacity of the BIAS before palletization is from about 1.0 to about 2.8mmol CO₂/g. Most preferred BIAS possess CO₂ capture capacity beforepelletization greater than about 2.8 mmol CO₂/g.

The physical characteristics of the BIAS are critical to theirincorporation into the pelletized sorbent. The BIAS powders arepreferentially 1 nm to 25 μm in diameter. Further, BIAS particles may beground prior to pelletization. Such grinding serves to process theparticles into a size preferential for incorporation into a pellet aswell as expose a greater number of functional groups for CO₂ capture.

Inorganic Strength Additives:

In addition to the Basic Immobilized Amine Sorbents, the pelletizedsorbents comprise one or more inorganic strength additives. Theinorganic strength additive provides a single or plurality of solidsubstrate which primarily serve to provide structural support to thepellet. As discussed supra, BIAS, when used directly in gas separationoperations, presents difficulties when used at an industrial scale.Thus, addition of an inorganic strength additive, in part, facilitatesthe structural integrity of the basic immobilized amine sorbent basedpellet thereby structural degradation and material loss is avoided.

Ideal inorganic strength additives are available in large quantity,inexpensive, do not drastically decrease the CO₂ capture capacity of thesorbents, and provide a medium capable of increasing the structuralintegrity of the pellet. Additionally, inorganic strength additivesideally are able to bond either chemically or physically to the otherconstituents of the pelletized sorbent. Exemplary inorganic strengthadditives, in addition to fly ash, include bottom ash; clays; activatedcarbon; and oxide materials themselves typically comprising fly ash,namely silicon dioxide, aluminum oxide, and calcium oxide.

In one embodiment, the inorganic strength additive is fly ash. Fly ash,also known as pulverized fuel ash, is commonly produced as a solidproduct of coal combustion where the fly ash is carried by and latercaptured from the flue gas. Fly ash is available in a variety ofdimensions and compositions.

Fly ash compositions include functional groups on the surfaces of thefly ash particles which promote agglomeration by chemical bonding. Forexample, select polymer binders may hydrogen bond to fly ash to promotethe formation of pellets and increase their end crush strength.Exemplary functional groups on the fly ash include hydroxyl groups,carboxylic acid groups, and oxides.

As shown in Table 1, fly ash as used in pelletized sorbents is primarilycomprised of silica and alumina. However, as a product of primarily coalcombustion, the exact composition of other potential fly ash materialsmay vary depending on the combustion source. Advantageously, both silicaand alumina can hydrogen bond to the amine groups of the sorbents andthe polymer binder to promote the formation of pelletized sorbent.Therefore, it is expected that other fly ash sources are capable ofassisting pellet formation for the sorbents.

TABLE 1 Fly ash major oxides content as wt % and mol %. Components wt. %mol. % Al₂O₃ 25.59 17.92 CaO 1.55 1.97 Fe₂O₃ 5.02 2.24 K₂O 2.92 2.21 MgO0.79 1.4 MnO 0.05 0.05 Na₂O 0.56 0.65 P₂O₅ 0.07 0.04 SiO₂ 61.02 72.52TiO₂ 1.11 0.99 Loss on Ignition 1.33

The dimensions (particle size) of the inorganic strength additive allowgreater incorporation of the strength additive into the other materialscomprising the pellet sorbent. Denser packing of smaller inorganicstrength additive particles between larger sorbent particles couldstrengthen the pelletized sorbent as previously stated. Inorganicstrength additive sizes range from about 1 nm to about 25 μm. In apreferred embodiment, inorganic strength additive particle sizes rangefrom about 1 nm to about 2.0 μm.

FIG. 2 shows the effect of the inorganic strength additive fly ash onthe average crush strengths (MPa in P_(crush)) of pellets prepared froma BIAS sorbent containing 50 wt % ethylenimine, MW=423/silica, labeledEI₄₂₃-S, or 50 wt % tetraethylenepentamine (TEPA)/silica, labeledTEPA-S. Crush strength of the final pelletized sorbent (pellets) is anaccurate measure of the structural integrity and mechanical strength ofthe material. Crush strength is defined and calculated as the pelletcrush weight divided by the cross-sectional area of the pellet(area=diameter times length). The crush weight is represented as anaverage of three crush tests, where the standard deviation is less than15%. In FIG. 2, the fly ash content is reported as X/Y (Y=100−X), whereX/Y is the wt % ratio of FA/sorbent in the dry mixture (FA plussorbent). This X/Y ratio does not include the content of the polymerbinder, or additional amine added together with the polymer binder tothe pellet. Overall the final composition of the pellets in FIG. 2includes 10 wt % polymer binder (poly (vinyl chloride), PVC), 5 wt % ofadded amine (TEPA), and between 8 wt % (X/Y=10/90) and 35 wt %(X/Y=40/60) fly ash. Increasing the strength additive (fly ash, averageparticle diameter=1.7 nm) content from X/Y=0 to 40 wt % forEI₄₂₃-S-based and TEPA-S-based sorbent pellets enhanced their mechanicalstrength by a factor of 1.9 and 3.1, respectively. Furthermore, densepacking of smaller strength additive (fly ash) particles (D_(P,avg.)=1.7μm) between larger sorbent particles strengthened the pellet bymechanically interlocking the particles, and also reducing voids thatwould weaken the pellet.

In the final pelletized sorbents (pellets), the inorganic strengthadditive may range from about 5 wt % to about 37 wt % of total drypelletized sorbent weight. Preferentially, the inorganic strengthadditive ranges from about 8 wt % to about 37 wt % of total pelletizedsorbent. More preferentially, the fly ash composition is from about 18wt % to about 37 wt % of total pelletized sorbent.

Polymer Binders:

In the pelletized sorbent, the Basic Immobilized Amine Sorbents andinorganic strength additives are agglomerated via at least one polymerbinder. Polymer binders serve to interconnect the respective componentsto form a rigid network suitable for structurally stabilizing the pelletthrough chemical, physical, or a combination of chemical and physicalbonding. In one example, the polymer binder polyvinyl chloride (PVC)operates by way of introducing a polymer network which physicallyentraps the BIAS and inorganic strength additive particles.

Pelletized sorbents may further comprise more than one polymer binder.As in Example 1, a single polymer binder such as PVC may be utilized.However, more than one polymer binder may be utilized. In Example 8, acombination of poly (chloroprene) latex and polyethylenimine isutilized.

The mechanism responsible for the agglomeration may be physical,chemical, or both physical and chemical. In physical agglomeration, theagglomerated components are physically intertwined by the polymerbinder. The binding polymer interactions, in part, create a network ofphysical cross-links which contribute to the pellet strength.

With respect to chemical bonding, the polymer binder functions primarilythrough two types of chemical interactions, hydrogen bonding (H-bonding)and covalent bonding (cross-linking). Hydrogen bonding in generalinvolves the electrostatic interactions between H atoms attached toelectronegative atoms such as N, O, and other electronegative atomsattached to molecules in close proximity. FIG. 3 (a) shows theinterconnected network of the BIAS pellets comprised of BIAS and fly ashas strength additives dispersed within a polymer binder. The schematicof FIG. 3 (b) shows that three different H-bonding mechanisms within thepellet are possible. Mechanisms (1) and (2) involve interactions betweenfunctional groups of the polymer binder chains and the surface hydroxylgroups (—OH) of either a silica-type support of the BIAS sorbent or thefly ash particles. The polymer binder possess functional groups, such aschlorine (—Cl) groups for PVC or poly (chloroprene) (PC), hydroxylgroups (—OH) for PVA, urethane (—NHCOO—R) groups for polyurethane (PU),or other electronegative atoms that interact with the H atoms of the flyash or silica —OH groups to adhere the polymer binder to the fly ash andsorbent.

The long polymer binder chains of the polymer binder entangle throughintermolecular or intramolecular H-bonding which further contributes tothe pellet strength. Mechanism (3) of FIG. 3(b) involves H-bondinginteractions between the polymer binder and the amines coated of theBIAS. Polymer binders, in addition to PVC and PC may adhere the pelletsthrough hydrogen bonding of their various functional groups.

In one embodiment, the polymer binders are hydrophobic. Hydrophobicpolymers can be described generally in three different ways, which arenot wetted by water, i.e. the contact angle of a small droplet isgreater than zero, not soluble in water, or minimally absorbing oradsorbing adsorb. In contrast, materials that are wetted by water,dissolve in water, or absorb water are considered hydrophilic.Hydrophobic polymers accompany material such as the poly(chloroprene)(PC), PVC, polystyrenes, polyurethanes, and epoxies. Hydrophobicpolymers are one method by which to impart the necessary hydrophobicityto the pellets. In another embodiment, the polymers are hydrophilic;wetted by water, dissolve in water, or absorb/adsorb water. Thesepolymers can include poly (vinyl alcohol), poly (vinylpyrrolidone), andpoly (acrylamide). To impart hydrophobicity to the pellet, a hydrophobicadditive such as those polymers previously mentioned would be includedin the BIAS. In general, pellets can be prepared either with ahydrophobic sorbent and a hydrophilic polymer binder, or a hydrophilicsorbent and a semi-hydrophobic polymer binder.

Preferred polymer binders include the following polymers, preferredfunctional groups of these and of modified versions of these polymersinclude the following: F (fluorine atom)-poly(vinylidene fluoride),poly(tetrafluoroethylene); acetal (RCOR)-poly(vinyl acetate); Cl(chlorine atom)-isoprene, polyisoprene, chlorinated polyethylene; ether(ROR)-poly(vinylbutyral),poly(vinylbutyral-co-vinylalcohol-co-vinylacetate), poly(vinylchloride-co-vinyl acetate-co-vinyl alcohol), poly(ethyl vinyl ether),poly(vinyl formal); ester (RCOOR)-polyester poly(tert-butyl acrylate),poly(vinyl cinnamate); carbonate (RCOO⁻)-polycarbonate, polypropylenecarbonate); carboxylic acid (RCOOH)-poly(vinylchloride-co-acrylic-acid); nitrile-poly(acrylonitrile), andpoly(acrylonitrile-co-butadiene); imide (RCO)₂NR; and amide (RCONR).Polymers containing any of these preferred functional groups isincluded. Co-polymers comprised of more than one of these preferredpolymers is also included.

Another preferred polymer binder and modified versions thereof ispoly(chloroprene) latex (PC latex). PC latex differs frompoly(chloroprene) pure polymers in the following ways: (1) PC latex is asuspension (emulsion) of nano-sized solid particles in water; therefore,it lends a slightly different binding mechanism to the pelletizedsorbent than pure PC polymer; (2) being that PC is in emulsion form itdoes not have to be dissolved into any solvent because it is already ina usable form, which is in contrast to the pure PC that has to be groundfrom large chunks into small particles and then dissolved in a solventto make the polymer binder solution; and (3) the PC latex is largelyhydrophobic but contains hydrophilic functional groups that allow it toexist in the latex/emulsion state and these groups help the PC latex bemore compatible to impregnated polyamines in comparison to pure PC. Tosummarize, although used in the same way as the pure PC, the PC latexhas a slightly different binding mechanism than the pure PC and moreimportantly it dramatically simplifies the pellet synthesis processbecause it does not require any special preparation of its correspondingpolymer binder solution; no special grinding or heating in toxic solventsteps.

In one example, poly (vinyl alcohol) (PVA), which has —OH groups andpoly (vinyl acetate) (PVAc), which has —OC═O— groups, are alternativesto PVC that can hydrogen bond to fly ash and BIAS to form pelletizedsorbents. The aryl groups of polystyrenes can interact with Si—OH groupsof amine/silica sorbents and also Al—OH groups of zeolite.

Physical modification of the constituents also promotes pelletizationvia increasing bonding among the polymer binder. Physically grinding theBIAS before pelletization exposes bulk amine groups previously insidethe sorbent pores. In one instance, the exposed, high-viscosity EI₄₂₃ ofthe pellets in FIG. 2 would interact with the PVC binder and resist thecompressive force during crush testing. In other words, available —NH₂and —NH groups of viscous immobilized amines, in general, play anincreased role in binding the pelletized sorbents. Furthermore, thestrength additive can also be ground for providing added pelletstrength.

Polymer binders may also be modified to include functional groups whichenhance CO₂ sorption. In one embodiment, polymer binders are modified tocomprise amine functional groups. During experimental studies,pelletized sorbents comprising PVC formed ammonium ions while heating atthe CO₂ desorption temperature of 105° C. for 100 min. Ammonium ionswere formed via protonation of the amines by HCl, which was generated,in part, by the elimination reaction of PVC with highly basic aliphaticamines of the BIAS sorbent or binder solution. These protonated aminescannot absorb CO₂ which decreases overall CO₂ capture capacity duringlong term cycling. Modification of PVC with a less basic aromatic amine,for example p-phenylenediamine (PPD), before pelletizing favors thesubstitution reaction to form —NH groups, which capture CO₂, and reducethe chlorine content of PVC. Reduced chlorine in the modified exemplaryPPD-PVC binder discourages the formation of harmful HCl during cyclingof the pelletized sorbent. Additional species that may be used to modifythe PVC binder in addition to PPD include aniline, o-toluidine,diaminotoluenes, n-methylaniline, and diphenylamine.

PVC may also be modified by reacting it with a strong organic orinorganic base or nucleophile in the liquid or solid phase, utilizingthe elimination reaction, where the resulting PVC will be dechlorinatedto form HCl. This HCl can then be neutralized by rinsing the modifiedPVC (initially solid or precipitated from solution) with an aqueousinorganic base solution. Organic nucleophiles may include linearpolyamines such as ethylenediamine, tetraethylenepentamine, andpoly(ethylenimine), and choline hydroxide. Inorganic nucleophiles/basesinclude sodium carbonate, sodium hydroxide, other metal-hydroxidespecies, potassium thiocyanate, sodium iodide.

Preferentially, pelletized sorbents comprise those polymer binders withchlorine groups such as PVC and PC. Other polymer binders include thehydroxyl group polymer PVA, followed by PVAc (acetate groups) thenpolystyrene (aromatic benzyl groups).

The pelletized sorbents are typically comprised of 1 to 15 weight % ofthe total dry pelletized sorbent as polymer binder. Preferential weightpercent . . . 5 to 8 wt %. Most preferential weight percent 8 to 15 wt%.

Additives:

In one embodiment, the pelletized sorbents contain additives. Across-linker additive introduces covalent bonding as a pellet bindingmechanism, attaching two or more polymer chains within the networktogether via the cross-linker. As shown in FIG. 4, polymer binder chainsare interconnected via chemical bonds with a cross-linker having atleast two reactive functional groups, one each bond to a polymer binder.Cross-linkers act beneficially to increase pellet mechanical strengthand also increase hydrophobicity. FIG. 4 (b) illustrates that pelletsbound with PVC are cross-linked with a diamine (NH₂—R—NH₂), where eachof the primary amine groups (—NH₂) chemically react with and joindifferent PVC chains. Exemplary amine molecules possessing two or more—NH₂ groups may include tetraethylenepentamine, polyethylenimine,phenylenediamine, and 1,6-hexanediamine.

Alternatively, pellets preferentially bound with PVA or a combination ofPVA and polyethylenimine (PEI) are cross-linked with a dialdehyde(OHC—R—CHO), where each aldehyde (—CHO) group reacts with different PVAchains via two hydroxyl (—OH) groups on each chain to form theinterconnected polymer network. A dicarboxylic acid could cross-linkPVA. Exemplary dialdehydes may include linear glutaraldehyde andaromatic, hydrophobic terephthalaldehyde.

Other preferred cross-linking compounds are molecules bearing more thanone epoxy group, such as different forms of bisphenol A diglycidylether(di-epoxy), N,N-Diglycidyl-4-glycidyloxyaniline (tri-epoxy), and4,4′-Methylenebis(N,N-diglycidylaniline) (quart-epoxy groups). Theseepoxies covalently join multiple amine molecules together to form anetwork. These amine molecules could be those of the BIAS sorbents beingpelletized, or could be additional amine species added together with theepoxy in the polymer binder solution. Other preferred cross-linkersinclude aminosilanes (with amine groups) or alkoxysilanes (without aminegroup) and possessing methoxy/ethoxy (ROCH₃/ROCH₂CH₃) group, suchas-aminopropyltrimethoxysilane, aminopropyltrimethoxysilane,N-(3-(trimethoxylsilyl)propyl)ethylenediamine,tetraethyeleorthosioicate. Commonly known cyanate/isocyanate(ROCN/RNCO), and acrylate and cyanoacrylate can also be used with apolyol (multiple —OH groups of an alcohol) molecule to covalent bind thepellet sorbent.

In one embodiment, loaded amines are additives to the pelletizedsorbents. The loaded amines are introduced to the pelletized sorbentcomposition during manufacturing as a part of the polymer bindersolution. The loaded amines are present throughout the pelletizedsorbent and serve to increase final CO₂ sorption capacity. Loaded aminesmay be present in the pelletized sorbent from up to about 8 wt % of thetotal pelletized sorbent. Other preferred additives include thefollowing: (i) antioxidants such as sodium carbonate, sodiumbicarbonate, potassium carbonate, other water-soluble metal-carbonates,phenylenediamine, and various aminoacids, (ii) CO₂ adsorption enhancerssuch as ethylene glycol, poly (ethylene glycol), and non-ionicsurfactants. One or more of these additives may be incorporated withinthe pelletized sorbent's base constituents to promote characteristicssuch as porosity, stability, or CO₂ migration through the pellet andalso incorporated within the binder solution.

Pelletized Sorbent Composition:

A salient aspect of the invention is the final pelletized sorbentcomposition. Primary parameters are the sorbent capacity of thepelletized sorbent, primarily as a result of the loaded BIAS andadditives, and the structural integrity of the pelletized sorbent, whichis primarily a result of the inorganic strength additives and theirinteraction with the binding polymers. Pellet composition is based uptotal dry pelletized sorbent weight, where dry weight includes the massof the BIAS, inorganic strength additive, polymer binder, and loadedamines.

The preferred pelletized sorbent composition range as the following:from about 63 to about 92 wt % as BIAS of total dry pelletized sorbentweight BIAS sorbent, from about 8 to about 37 dry weight % as fly ash oftotal dry pelletized sorbent weight, 5 to 13 dry wt % as polymer binderof total dry pelletized sorbent weight. In another embodiment, additivespresent in pelletized sorbents up to about 8 wt % as loaded amine oftotal dry pelletized sorbent weight. Preferred BIAS composition of totaldry pelletized sorbent weight is 50 to 68 wt %. Most preferred BIAScomposition of total dry pelletized sorbent weight is 68 to 85 wt %.

The pelletized sorbents demonstrate high CO₂ capture capacity in wt % ormmol CO₂/g-pellet) relative to their total dry pelletized sorbentweight. As expected, an increasing wt % of inorganic strength additivewith the corresponding decrease wt % of BIAS results in a decreasing CO₂sorption. To illustrate, reduction in CO₂ capture capacity for flyash/EI₄₂₃-S and fly ash/TEPA-S pellets with increased fly ash contentresulted from the replacement of the amine sorbents with fly ash, whichonly captured 0.01 mmol CO₂ g⁻¹. The combination of strength and CO₂capture for fly ash/EI₄₂₃-S (20/80) PVC₆₂ and fly ash/TEPA-S (30/70)PVC₆₂ summarized in Table 2 demonstrate the pelletized sorbents(especially the former) are attractive for long-term stability use.

TABLE 2 Performance and composition of optimized FA/EI₄₂₃-S andFA/TEPA-S (X/Y)_PVC₆₂ pellets. Values for pellets without FA and for thecorresponding particle sorbents are included for comparison. Bindercontent: CO₂ PVC₆₂/FA/ capture Crush TEPA(loaded) (mmol strengthMaterial (wt %) CO₂ g⁻¹)^(]) (MPa) EI₄₂₃-S (50 wt % EI₄₂₃/silica) 2.90TEPA-S (50 wt % TEPA/silica) 2.91 FA/EI₄₂₃-S 10/0/5 1.79 1.07 (0)_PVC₆₂FA/TEPA-S 10/0/5 1.51 0.46 (0)_PVC₆₂ FA/EI₄₂₃-S 10/17/5 1.33 1.42(20/80)_PVC₆₂ FA/TEPA-S 10/25/5 1.10 1.13 (30/70)_PVC₆₂

Pelletized Sorbent Performance:

The pelletized sorbent CO₂ sorption capacity is primarily a function ofthe BIAS and any amine bearing additives, where as noted above thesorption capacity is the ability of the pelletized sorbent to adsorb andseparate an amount of CO₂ from a gaseous mixture. The sorption capacityof the pelletized sorbents is typically greater than 1.0 mmol/g.Preferentially, the sorption capacity of the pelletized sorbents isgreater than 1.7 mmol/g. More preferentially, the sorption capacity ofthe pelletized sorbents is greater than 2.0 mmol/g. FIGS. 2, 8, 10, and11 show the CO₂ capture capacities (mmol CO₂/g) of different pelletizedsorbents comprised of various BIAS and polymer binders, and alsocontaining a range of fly ash content (wt %).

Another salient aspect of the invention is that the pelletized sorbentis hydrophobic in that it repels H₂O vapor or condensed H₂O (liquidH₂O), thus preserving the CO₂ capture capability of the pellet. As notedpreviously, a disadvantage of the current stand-alone BIAS is that theyare vulnerable to leaching from the sorbent pores by condensed steamduring practical CO₂ adsorption-desorption testing under humidifiedconditions. However, the negative effect of steam in the gaseous mixtureis remedied by the incorporation of the hydrophobic polymer binder tothe BIAS in the pelletized sorbent. The hydrophobic polymer binderminimizes contact between the pelletized sorbent's amines and condensedsteam during CO₂ capture cycling under practical humid conditions. Thishydrophobicity extends the lifetime of the pelletized sorbent.

In one test, the CO₂ capture capacity of the pelletized sorbentFA/EI₄₂₃-S (20/80) PVC₆₂ after being exposed to 0.5 mL/min of flowingwater for 40 min (a published accelerated H₂O testing method) was 71% ofthat for the fresh sorbent, where the PCR value used to assess pellethydrophobicity is calculated by dividing the pellet or particle sorbentCO₂ capture capacity after accelerated H₂O testing by the capacity ofthe fresh materials and multiplying by 100. This high percentage ofaccelerated H₂O CO₂ capture retained (further described as PCR unlessotherwise noted) value for the pellet, compared to only ˜3% for theEI₄₂₃-S particle sorbent, shows that PVC served as a hydrophobic pelletbinder. It was shown in the literature that there is a directcorrelation between the accelerated H₂O PCR values and the stabilitiesof BIAS material to H₂O vapor during practical steam testing at hightemperatures (55-105° C.) for 10-30 hr. These temperatures are in therange of those encountered during practical CO₂ adsorption-desorptioncycle testing. The reduced CO₂ capture of the pelletized sorbent afteraccelerated H₂O testing is a result of amine leaching from the BIASmaterial and likely rearrangement of the amines within the sorbentstructure. These degradation mechanisms are also encountered duringpractical testing under steam conditions. Typical pelletized sorbentsexhibit a PCR value of greater than about 20%. In a preferredembodiment, the pelletized sorbents exhibit a PCR of greater than 50%.More preferred pelletized sorbents exhibit a PCR of greater than 60%.

Another salient point of the disclosed pelletized sorbent is thestructural integrity of the pellet. The pelletized sorbent may have acrush pressure (P_(crush)) of 0.2 to 6 MPa, where crush pressure isdefined as (P_(crush)=F_(weight)/(D_(pellet)*L_(pellet)), whereF_(weight)=the crush force, D_(pellet)=pellet diameter andL_(pellet)=pellet length, as measured by micro-calipers. The calipershave a precision of 0.01 mm. In one embodiment, the pelletized sorbentshave a P_(crush) greater than 0.3 MPa. Preferentially, the pelletizedsorbents have a P_(crush) greater than 1.0 MPa. More preferentially, thepelletized sorbents have a P_(crush) greater than 1.3 MPa.

Preferred pelletized sorbents comprised of the BIAS, inorganic strengthadditive and polymer binder possess a CO₂ capture of greater than 1.7mmol CO₂/g, a PCR greater than 50%, and a P_(crush) greater than about1.0 MPa. More preferred, the hydrophobic pelletized sorbents possess aCO₂ capture of greater than 2.0 mmol CO₂/g, a PCR value greater than50%, and a P_(crush) greater than about 1.3 MPa.

Three exemplary methods of formation of pelletized sorbents aredisclosed. These methods involve (i) impregnating liquid amines intoalready fabricated pellets comprising the inorganic strength additiveand polymer binder (ii), mechanically compressing BIAS/inorganicstrength additive/polymer binder mixtures, and (iii) shaping wet pastescomprised of amine sorbent/inorganic strength additive/polymer bindersolution into pellets by extrusion or mold-casting.

In performing one example of method (i), a support structure for thepellet would be first prepared by combining a ground silica support andstrength additive powder, primarily fly ash, with a polymer bindersolution containing 5 to 20 wt % polymer binder (primarily poly (vinylchloride) or poly (chloroprene)) and potentially a polyamine amine,dispersant, or pore former to facilitate porosity throughout the polymerbinder for CO₂ transport through the pellet. The resulting pastes wouldbe extruded into ropes, and the resulting dry rods would be dried at 25to 105° C. It can be inferred that the —Cl groups of the chlorinatedpolymer binder would interact with silica and any binder additives toadhere the particles. Once dried, these pellet supports would be mixedwith an impregnation solution containing amine species typical of theBIAS sorbents, such as TEPA or PEI, epoxy-based cross-linkers, andantioxidants as previously mentioned, plus a solvent. The finalcomposition of the dry pellets would be 5-15 wt % polymer binder plusdispersant/pore former, 5-25 wt % strength additive, 0-5 wt %epoxy-based cross-linker, 0-5 wt % antioxidant, and the balance ofsilica plus impregnated amines.

Pelletization of BIAS sorbents by method (ii) would be accomplished byfirst preparing dry mixtures containing BIAS sorbent, strength additive(namely fly ash), and the polymer binder in fine powder or particle formThe dry mixtures would be placed into a cylindrical or other-shaped moldat 25° C. or at elevated temperature and compressed between 1,000 andless than 5,000 psig to form the resulting hydrophobic pellets. It isexpected that Class 1 sorbents (polyamine/silica), as previouslydescribed, would form stronger pellets than those of Class 2 sorbents(aminosilane/silica), due to even distribution of the higher-viscositypolyamines within the pellet. The polyamines would presumably existslargely inside the sorbent and pellet pores, and allow the pellet toresist compression due to capillary forces among theamine-silica-strength additive-polymer binder network and also the Class1 amine's high viscosity.

Although more complex than method (ii), pelletization of sorbents bymethod (iii) is attractive for large scale processes because of theability to maintain continuous extrusion and formation of sorbent drycomponent/polymer pastes into pellets. Therefore, this method isprimarily used to prepare the polymer binder/fly ash/BIAS pellets and isfurther illustrated in FIG. 5.

FIG. 5 shows an exemplary procedure for pelletizing the different BIASsorbents with a poly (vinyl chloride) polymer binder according to method(iii). Step 1 involves preparing the binder solution with differentconcentrations (5-10 wt %) of PVCX (x=Mw: 43 k, 62 k, or 80 k) and TEPA(0-5 wt %) dissolved in tetrahydrofuran (THF). In step 2, 1.0 g of theground sorbents was mixed with FA at FA/sorbent weight ratios from 0/100to 100/0. A 0.8-1.2 g amount of each binder solution was added to 1.0 gof the FA/sorbent mixtures to form pastes, which were extruded intoropes in step 3. In step 4, the wet ropes were either dried at 25° C.for 120 min or dried at 25° C. for 60 min followed by 105° C. for 12min, and broke into cylindrical pellets (D˜1.4-1.2 mm, L˜5 mm). Apotential cross-linking reaction between the amine (TEPA shown) and PVCwould join the polymer chains and enhance the mechanical strength of thepellet.

Preparation of BIAS pellets by method (i) can have advantages overmethod (iii), especially where faster CO₂ adsorption kinetics arenecessary. Furthermore, this method facilitates better control over thepellet structure in which the BIAS-based formula will be deposited,compared to that of method (iii).

FIG. 13 shows an exemplary, representative procedure for preparing BIASpellets via method (i), utilizing a polychloroprene latex binder. Asnoted, PC latex is an emulsion of H₂O-insoluble polychloropreneparticles suspended in water containing stabilizing additives. The PCpolymer may be anionic, cationic, or neutral and have chemicalstructures resembling 1,3-butadiene, 2,3-dichloro polymer with2-chloro-1,3-butadiene, and 1,3-butadiene, 2-chloro-homopolymer. Thesestructures may also be combined with rosin and talc and other additivesin the overall emulsion. Specifically tested were Showa-DenkoChloroprene Rubber Latex 671A, 571, and 400, which are allanionic-based. But any brand of PC latex is suitable. The latex form ofpolychloroprene greatly simplifies pellet preparation, making it moreattractive for scale-up. The pellet supports were synthesized from anarray of polymer binder solutions, which contained 4-8 wt % of acombination of the most thermally stable PC latex, type 400 (PC₄₀₀,Showa-Denko) and E100, PEI₈₀₀, PEI_(25 k), or PEI_(50 k) at latex/amineratios of 2/1, 1/1, and 1/2. 13.0 to 16.5 g of the binder solutions wereeach mixed with 5.0 g of dry mixtures of ground silica (particlesize=5-100 microns)/fly ash (FA) (10/90 wt. ratio) to form the wetpastes, which were syringe-extruded into rods. The 1.3-1.8 mm diameterrods were then dried at 105° C. for 70 min, broken into ˜5 mm lengths,then functionalized with PEI₈₀₀/E3 or E100/E3 mixtures. Impregnation ofthe optimum pellet supports was carried out by mixing 2.0 g of supportswith 20-21 g of impregnation solution containing amine, tri-epoxidelinker (N—N-diglycidyl-4-glycidyloxyaniline, E3), and K₂CO₃ antioxidantin MeOH, or mixtures of MeOH and DI water when K₂CO₃ is present. Thetotal amount of impregnated species on the pellet supports was variedbetween 20 and 30 wt %, where the ratio of E3/amine was adjusted between0 and 5 wt % and the K₂CO₃ content was between 0 and 2 wt %.

Noteworthy, pellets were prepared from PC₄₀₀ latex via method (iii).While displaying CO₂ capture between 1.0 and 1.8 mmol CO₂/g, thesepellets exhibited lower strength and slower CO₂ capture kinetics thanthose prepared by method (i). Therefore, pelletization by method (iii)is preferred.

EXAMPLES Example 1: Poly (Vinyl Chloride) (PVC) Binder

Pellet Preparation

Pelletization of sorbents was accomplished by first grinding the 100 μmsize particle BIAS into ≤25 μm size powders, which was verified by bothoptical microscope and particle size distribution analysis via dynamiclight scattering. The powder sorbents were homogeneously mixed withClass F fly ash (FA) powder (FA, D_(P,avg.)32 1.7 μm) at 0/100-100/0FA/sorbent weight ratios. Poly (vinyl chloride) (PVC)-based polymerbinder solutions were prepared by dissolving different molecular weightsof the hydrophobic polymer (Mw=43,000 g gmol⁻¹, PVC₄₃; Mw=62,000 gPVC₆₂; Mw=80,000 g PVC₈₀, Sigma-Aldrich) (0.5 g) into tetrahydrofuran(THF, anhydrous, Sigma-Aldrich) (4.25 g) at 50° C. followed by addingTEPA as a loaded amine (0.25 g) to the PVC/THF mixture. TEPA providesamines sites for both CO₂ adsorption and inter-particle CO₂ diffusionthrough the pellet. Multiple 1.2 g amounts of the binder solution weremixed with 1.0 g portions of each FA/sorbent mixture in a fume hood toform pastes. Rapid evaporation of THF while mixing resulted in a wetbinder/dry powder ratio of 0.7/1.0 for the pastes, which weresyringe-extruded into ˜1.6 mm diameter ropes. The ropes were dried at25° C. for 3 hr and then at 105° C. for 12 min, producing dry pelletrods that were broken into ˜3-6 mm lengths. The dry pellets containedabout 10 wt % PVC, 0-34 wt % FA, 5 wt % TEPA (from binder soln.), and51-85 wt % of the amine/silica BIAS sorbent. The pellets were named withthe scheme, FA/Sorbent (X/Y) Polymer, where X/Y (Y=100−X) are the wt %of FA/sorbent in the dry powder (FA plus sorbent) and Polymer is 10 wt %as the polymer binder.

Pellet Performance

Results for CO₂ capture capacities and crush strengths of the PVC-basedpellets containing various fly ash contents was previously discussed andcan be seen in FIG. 2. A preferred PVC-based pellet, FA/EI₄₂₃-S (20/80)PVC₆₂, contained about 17 wt % fly ash and about 10 wt % PVC, andcaptured 1.33 mmol CO₂/g and had as crush strength of 1.42 MPa. Thehigher mechanical strengths for the EI₄₂₃-S pellets than for the TEPA-Spellets are attributed to the higher viscosity of the EI₄₂₃ amine thanthat of TEPA. The higher viscosity creates a strong resistance to thecompressive forces during crush testing.

Example 2: p-Phenylenediamine (PPD)-Modified PVC Binder

Pellet Preparation

In step 1, 1.0 g of PVC (Mw=62,000) was dissolved in 15.0 g oftetrahydrofuran (THF) on a hotplate at 45° C. followed by the additionof p-phenylenediamine (PPD) to the PVC/THF mixture. Four differentmixtures were prepared by varying the amount of PPD to give—NH₂(PPD)/—CHCl (PVC) molar ratios of 0.5, 0.6, 1.0, and 2.0. Theresulting PVC/PPD/THF mixtures were reacted at 45° C. for 1-1.5 hr,which formed dark red/brown semi-viscous solutions. Step 2 involvedadding the viscous solutions to 200 mL of ethanol (EtOH) under mixing,which precipitated light-pink PPD-modified PVC. In step 3 theprecipitates were filtered, and then twice washed with EtOH andfiltered. Lastly in step 4, the cleaned PPD-modified PVC materials wereair dried overnight (17 hr) and then oven dried at 105° C. for 12 min toremove the remaining EtOH. Pellets containing the PPD-modified PVC wereprepared using a similar procedure as that for the PVC pellets. Multiple1.2 g amounts of solutions containing 10 wt % PPD-modified PVC/5 wt %TEPA/THF were mixed with separate 1.0 g portions of the FA/EI₄₂₃-(20/80)dry mixture to form the pastes, which were extruded and dried to givethe final cylindrical pellets.

Pellet Performance

Results showed that the pellet prepared from the 0.6 molar ratio —NH₂(PPD)/—CHCl (PVC₆₂), labeled as FA/EI₄₂₃-S (20/80) PPD-PVC₆₂, captured1.51 mmol CO₂/g and had a crush strength of 1.32 MPa. Furthermore,diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)revealed that the PPD-PVC binder produced a pellet less prone to formingammonium ions (—NH₂ ⁺, —NH₃ ⁺) than the pellet prepared from PVC. FIG. 6shows a slower increases in both the —NH₃ ⁺ species (2476, 2510 cm⁻¹)and the —NH₂ ⁺ (2098, 2095 cm⁻¹) for the PPD-PVC-based pellet than thePVC-based pellet, which confirms the better stability of the former.Furthermore, the higher CO₂ capacity for this pellet indicates thatamine groups of the PPD-PVC played a role in CO₂ capture or diffusionthrough the pellet.

Example 3: Poly (Chloroprene) (PC) Binder

Pellet Preparation

In one exemplary procedure, the ground EI₄₂₃-S sorbent (D_(p)<25 μm) wasmixed with fly ash (FA) at FA/sorbent ratios of 10/90 and 20/80 to formthe dry mixtures. FIG. 7 shows that pelletization of the dry mixtureswith a poly (chloroprene) polymer binder (PC) (Sigma-Aldrich, Mooneyviscosity=40) was accomplished in four steps.

Step 1 was preparing the binder solution by mixing 0.48 g of PC in 3.15g of 1,4-dioxane on a hotplate set at 50° C. for 30-90 min to form aviscous solution or low viscosity gel, and then adding TEPA ifnecessary. In step 2, 0.7-0.85 g of the PC binder solution was mixedwith 1.0 g of each FA/sorbent dry mixture to form pastes, which wereextruded into ropes in step 3. In step 4, the wet ropes were either (b)spheronized or (a) not spheronized and then dried at 25° C. for 60 minfollowed by 105° C. for 60 min. The resulting dry rods (not spheronized)were broke into cylindrical pellets (D˜1.7 mm, L˜5 mm).

In another exemplary procedure, pelletization of dry mixtures of FA andground 50 wt % ethylenimine E100 (Huntsman)/silica (E100-S),FA/EI100-S=120/80 and 10/90 with the poly (chloroprene) polymer binder(PC) (Sigma-Aldrich, Mooney viscosity=40) was accomplished in foursteps. Step 1 was preparing 4.0 g batches of different binder solutionscontaining 10-13 wt % PC dissolved in 1,4-dioxane for 20-60 min using anoil bath at 105° C. Depending upon the dissolving time, different bindersolution consistencies were obtained and ranged from thick viscous gelsto medium viscosity solutions. In step 2, 1.1 g of each PC solution wasmixed with 1.0 g amounts of the FA/sorbent dry mixture to form a wet orputty-like paste, which was extruded into ropes in step 3. In step 4,the ropes were dried at room temperature for 1 hr then dried at 105° C.for 1 hr. The final pellets contained 17-18 wt % FA, 10-13 wt % PC, andthe balance of sorbent. The pellets were simply labeled according totheir nominal PC wt % and mixing time.

Pellet Performance

Table 3 shows the performance of the FA/EI₄₂₃-S/PC pellets prepared withsimilar wt % of poly (chloroprene) polymer binder, where thecorresponding PC/dioxane binder solutions were mixed at 50° C. fordifferent times. The binder solutions of these pellets do not have TEPA.

TABLE 3 CO₂ capture capacity and mechanical strength of pellets preparedwith nominal compositions of 70-75 wt % of 50 wt % EI₄₂₃/silica BIASsorbent 7-9 wt % poly (chloroprene) (PC), and 8-19 wt % fly ash (FA).Crush strength was determined as the point of complete pellet crushingor at ~50% pellet compression. Binder mix PC/FA Initial CO₂ ads. Crushpressure Pellet time (min) (wt %) (mmol CO₂/g) (MPa) P1 90 9.1/18.2 1.440.91 (flexible) P2 40-55 8.5/18.3 1.65 1.20 P3 40-55 7.2/18.6 1.67 1.08P4 30 8.7/18.3 1.37 1.57 (rigid) P5 30 8.4/9.2  1.61 1.12

All pellets prepared with PC exhibited CO₂ capture capacity between 1.4and 1.7 mmol CO₂/g and varying crush strengths, which depended upon thebinder mixing time and fly ash content. Pellets 1-4 show that decreasingthe mixing time enhanced the crush strength from 0.91 to 1.57 MPa.

FIG. 8 shows the CO₂ capture capacities of the P2-P5 pellets BIASsorbent during 10 CO₂ adsorption-desorption cycles. Cycles wereperformed in a thermogravimetric analyzer (TGA) by (i) pretreating at105° C. for 10 min in 60 mL/min flowing N₂, (ii) flowing 60 mL/min of14% CO₂/N for 10 min at 55° C. for CO₂ adsorption, (iii) switching theflow to 60 mL/min N₂ for 10 min for pressure swing CO₂ desorption, and(iii) heating at 105° C. for 10 min in the N₂ flow for combinedtemperature and pressure swing CO₂ desorption. All pellets exhibitedstable CO₂ capture capacities during the 10 adsorption-desorptioncycles, showing promise for the application of FA/BIAS/poly(chloroprene) pellets to large scale processes.

Pellets prepared with the FA/E100-S dry mixtures and different amountsof PC, where PC was dissolved in the binder solutions for 20-30 min,exhibited different physical characteristics and CO₂ uptake kinetics andcapacities. The pellets prepared from FA/E100-S (20/80) dry mixturescontained between 12 and 13 wt % PC, with 12.2 wt % PC. FIG. 9 revealsthat dissolving the PC for different times produced slight butnoticeable changes in the pellet CO₂ uptake kinetics and final CO₂capture capacities. One preferred pellet was prepared with a bindersolution mixing time of 20 min, and was labeled “12.2 wt % PC_20 min” inFIG. 9. This pellet contained about 17 wt % fly ash, 12.2 wt % PC, andthe balance of the FA/E100-S dry mixture and captured 1.76 mmol CO₂/g.Given the optimum PC content for the 17 wt % fly ash pellet, a pelletwas prepared with lower fly ash content, about 8 wt % fly ash, 12.2 wt %PC, and the balance of E100-S, and was labeled FA/E100-S (10/90)_PC(12.2). Similar to the EI₄₂₃-S based pellets, the FA/E100-S (20/80)_PC(12.2) pellets underwent cyclic CO₂ capture studies in the TGA system.The results of the cyclic study, shown in FIG. 10, reveal that theFA/E100-S (20/80)_PC (12.2) and FA/E100-S (10/90)_PC (12.2) pelletsexhibited highly stable CO₂ capture capacities of around 1.76 (2.4% CO₂capture decrease from 1.79 to 1.74 mmol CO₂/g) and 1.98 (2.7% increasefrom 1.97 to 2.04 mmol CO₂/g) under dry conditions. Furthermore,accelerated H₂O PCR values for FA/E100-S (20/80)_PC (12.2) and FA/E100-S(10/90)_PC (12.2) were 55.5% and 57.3% respectively, compared to 3% forthe E100-S sorbent, confirming that poly (chloroprene) served as ahydrophobic polymer binder. These data indicate that the pellets willhave stable performances during cycling in the presence of H₂O vapor.

Cyclic testing of the FA/E100-S (20/80)_PC (12.2) pellet underpractical, humid conditions was accomplished by placing 0.85 g ofpellets into a ¼″ diameter fixed bed reactor; pre-treating the pelletsat 105° C. in 100 mL/min flowing He for 20 min; switching the flow fromHe to either 10% CO₂/He (dry cycles) or CO₂/He/˜5% H₂O (wet cycles) for20-25 min for CO₂ adsorption; switching the flow back to He for removalof weakly adsorbed CO₂ by pressure swing for 12-15 min; and then heatingto 105° C. and holding at 105° C. for 20-25 min for combinedtemperature/pressure swing desorption of strongly adsorbed CO₂. CO₂capture capacity and fixed bed reactor steam PCR (steam PCR) value ofthe pellets were calculated from the effluent CO₂ gas concentrationduring the CO₂ adsorption step of the two dry cycles before and afterthe wet cycles. Gas profiles were measured by a mass spectrometerlocated after the reactor. The 7 total cycles took 13 hr, with 6 hrexposure of the pellets to a humid environment. Results showed that theCO₂ capture capacity of the pellet decreased by only 4% steam PCR=96%),from 1.74 mmol to 1.67 mmol CO₂/g, after testing and confirms the robustnature of the combination of FA, PC, and BIAS to produce a strong,stable, and hydrophobic pellet.

The FA/PC/BIAS pellets exhibited good flexibility, so attrition testingof the pellet was performed instead of crush testing to assess pelletmechanical strength. The attrition test was modified from two ASTMstandards, E728-91 and D4058-96. For the test here, 2.0 g of pellets and20 g of 3/16′ metal ball bearings (about 46 ball bearing) were placedinside of a glass jar (diameter=7.3 cm, length=9.1 cm) containing a 0.5″protruding baffle along the full length of the jar. The jar and itscontents were rotated at about 39-40 rpm for 24 a period of hours, andthe attrition of the pellets was calculated by measuring the weights ofboth fine particles broken away (attritted) and the remaining intactpellets. Results showed that the pellets attritted less than 0.5% afterthe 24 hr, indicating that the pellets could remain intact during CO₂adsorption-desorption cycling in a moving bed reactor system. The 0.5%attrition is significantly less than the ˜17% and 81.5% attritionobserved for some commercially available silica pellets after only 1 hr,which confirms the superior strength of the PC/fly ash combination overcurrently available materials.

Example 4: Polyurethane (PU) Binder

Sorbent EI₄₂₃-S was ground to <25 μm (optical microscope) and mixed withfly ash (FA) at a FA/sorbent ratio of 20/80 to form the dry mixture.Five binder solutions were prepared by mixing 1.3 g of differentpolyurethane (PU) dispersion solutions (40 wt % PU/H₂O, Bayer) with 6.6g H₂O and then adding 0.22 g tetraethylenepentamine (TEPA, technicalgrade). The five PU binder solutions were prepared with Bahydrol 124(anionic dispersion, aliphatic polycarbonate urethane), Bahydrol 140 AQ(anionic dispersion, aliphatic polyester urethane), Bayhydrol XP 2637(anionic dispersion, aliphatic polycarbonate urethane), Bayhydrol UH XP2719 (anionic dispersion, aliphatic polyester-based), and Baybond PU 406(non-ionic polyurethane). A 0.9 g amount of each binder solution wasmixed with 1.0 g of the dry sorbent/FA mixture, and the resulting pastewas extruded into 1.5-2.0 mm diameter wet ropes. The wet ropes weredried at 100° C. for 60 min to form the 1.5-2.0 mm diameter pellets,which were broken into 3-6 mm lengths. Table 4 shows that pelletsprepared with polyurethane as a hydrophobic polymer displayed modest CO₂capture and acceptable crush strength. These data show that although PUcan also serve as a polymer binder for polymer/FA/BIAS pellets.

TABLE 4 CO₂ capture capacities of pellets prepared with differentpolyurethanes as either a hydrophobic polymer binder, or hydrophobicBIAS additive. Solid CO₂ capture Crush polymer Fly ash mmol CO₂/pressure Pellet Solid polymer (wt %) (wt %) g-pellet. (MPa) P1 BayhydrolPU 2719 12.3%  8.6% 1.15 0.61 P2 Bayhydrol PU 2719 8.1% 9.1% 1.22 0.51P3 Baybond PU 406 7.8% 9.1% 0.37 P4 Bayhydrol 140 AQ 8.1% 9.1% 1.12<0.13* P5 Bayhydrol 124 7.5% 9.1% 1.33 <0.13* P6 Bayhydrol XP 2637 7.7%9.1% 1.22 <0.13* P7 Cross-linked PVA 5.1% 18.6%  0.89 1.47 (Mw = 89,000)*Minimum crush pressure that can be applied by the bench-top tester. Theactual crush pressure is less.

Example 5: Polyurethane Additive to Amine/Silica BIAS Sorbent, with aCross-Linked Poly (Vinyl Alcohol) Binder

Polyurethane UH XP 2719 was also used as an additive to produce ahydrophobic sorbent that could be pelletized with poly (vinyl alcohol)(PVA), which is a hydrophilic polymer binder. A sorbent consisting ofPEI₈₀₀/Bayhydrol UH XP 2719/silica-36/4/60 by weight, labeled NETL 96D,was prepared using the previously described wet impregnation method. Thepolymer binder solution was prepared by combining two solutions.Solution 1 contained 0.25 g polyethylenimine MW=2,000 (PEI₂₀₀₀, Aldrich)dissolved in 2.22 g H₂O. Solution 2 contained 0.26 g PVA Mw=89,000(PVA_(89 k), Aldrich) and 0.09 g of a 25 wt % glutaraldehyde (GA)solution (Aldrich) dissolved in 2.22 g H₂O. Solution 2 was heated at 80°C. for 30 min to pre-cross-link PVA and glutaraldehyde. Glutaraldehydeis a dialdehyde that can join PVA-PVA chains via C—O—C linkages, andalso join PEI-PEI and PVA-PEI polymer chains, all which contribute tothe pellet strength. Solutions 1 and 2 were combined to form the totalbinder solution, where 0.65 g of the solution was mixed with 1.0 g of aFA/NETL 96D-20/80 dry mixture to form a paste. The paste was extrudedinto 1.5-1.9 mm diameter ropes, which were dried at 105° C. for 60 minand broke into 3-6 mm lengths to form the final pellets. The CO₂ captureof the pelletized FA/sorbent mixture was a low 0.89 mmol CO₂/g, whileexhibiting a crush strength comparable to PVC and PC (Table 4). Thesedata show that pelletization of FA/BIAS combinations can involve eithera hydrophobic polymer binder, such as PVC or PC, when the BIAS ishydrophilic or a hydrophilic polymer binder, such as PVA, when the BIAScontains a hydrophobic BIAS additive, such as polyurethane.

Example 6 Additional Polymer Binders

The FA/EI₄₂₃-S (20/80) dry powder was also pelletized with 10 wt % ofnon-cross-linked poly (vinyl alcohol) [PVA₆₇ (Mowiol 8-88) andPVA₈₉₋₉₈], polystyrene (PSt₃₅), and poly (vinyl acetate) (PVAc₁₀₀),along with 5 wt % TEPA both on a dry pellet basis. A similar procedureas that for the PVC-based pellets was used to prepare pellets with theseadditional polymer binders. These polymer binders illustrate theversatility of the pelletized sorbents using a variety polymer binderswith different properties and hydrophobicity/hydrophilcity. About 1-1.2g of each polymer binder solution containing 10 wt % of PVA (H₂Osolvent), PSt (THF solvent), or PVAc (EtOH solvent) and 5 wt % TEPA wasmixed with 1.0 g of the FA/EI₄₂₃-S (20/80) dry mixture, extruded, andthen dried to form the final pellets. The pelletized sorbent performanceis illustrated in FIG. 11.

Example 7: BIAS Sorbent Preparation with an Epoxide-Based Cross-Linker

Sorbent Preparation

Sorbents containing amine plus epoxide-based cross-linker were preparedby first dissolving 4.0 g of PEI₈₀₀ plusN—N-diglycidyl-4-glycidyloxyaniline (E3) in 100 g of MeOH, where theE3/PEI weight ratio was varied between 0 and 1.5. The resultingimpregnation solution was mixed with 6.0 g of PQ CS 2129 SiO₂(D_(p,avg.)=100 μm) inside of a 250 mL round-bottom flask. The flask wasconnected to a rotary evaporator set at 40° C. and 100 rpm, and thesolvent was evaporated for 60 min by sequentially reducing the systempressure from 300 mm Hg to 30 mmHg at a step-wise rate of 100-150 mmHgevery 25-30 min. Once the solvent was evaporated, the 100 μm sizeparticle sorbents were removed from the flask and placed in sealedvials, which were heated in an oven at 105° C. for 60 min to completethe PEI-E3 reaction.

Sorbent Performance

FIG. 12 shows the PEI/E3/SiO₂ sorbents' CO₂ capture capacities, plustheir accelerated water PCR and OCR (organic content retained) values.OCR was calculated by, (Organic content,_(Fresh)−Organiccontent,_(Washed))/Organic content,_(Fresh)×100%. The data clearly showsthat increasing the E3/PEI ratio dramatically enhances the H₂O stabilityof the sorbents, giving an optimum CO₂ capture capacity of about 1.6mmol CO₂/g and optimum PCR/OCR values of 55.8%/87.6% at an E3/PEI ratioof 0.28.

Example 8 Method (i) Pelletization with Polychloroprene Latex,Incorporating Epoxide-Based Cross-Linker and/or K₂CO₃ Antioxidant

Pellet Preparation

FIG. 13 shows that the pellet supports were synthesized from an array ofpolymer binder solutions, which contained 4-8 wt % of a combination ofPC latex type 400 (PC₄₀₀, Showa-Denko) and E100, PEI₈₀₀, PEI_(25 k), orPEI_(50 k) at latex/amine ratios of 2/1, 1/1, and 1/2. 13.0 to 16.5 g ofthe binder solutions were each mixed with 5.0 g of dry mixtures ofground silica (particle size=5-100 microns)/fly ash (FA) (10/90 wt.ratio) to form the wet pastes, which were syringe-extruded into rods.The 1.3-1.8 mm diameter rods were then dried at 105° C. for 70 min,broken into ˜5 mm lengths, then crush tested. Results of pelletpreparation and crush testing revealed that the optimum binder solutioncontained 6 wt % of PC₄₀₀/PEI_(25 k) at a 1/1 ratio. Impregnation of theoptimum pellet supports was carried out by mixing 2.0 g of supports with20-21 g of impregnation solution containing amine, tri-epoxide linker(N—N-diglycidyl-4-glycidyloxyaniline, E3), and K₂CO₃ antioxidant inMeOH, or mixtures of MeOH and DI water when K₂CO₃ is present. The totalamount of impregnated species on the pellet supports was varied between20 and 30 wt %, where the ratio of E3/amine was adjusted between 0 and 5wt % and the K₂CO₃ content was between 0 and 2 wt %.

Pellet Performance

FIG. 14 shows that raising the tri-epoxide E3 content of the 30 wt %impregnated pellets without K₂CO₃ gives higher CO₂ capture capacitiesand organic contents after flowing 20 mL of water at 0.5 mL/min over 0.5g of the sorbent (accelerated H₂O testing). This enhanced waterstability lead to increased OCR and PCR values for the pellet sorbents,similarly as was observed for the particle sorbents. OCR values werebased upon the amounts of organic impregnated into the pellet supports,as the pellet supports themselves lost less than 2% of their organicsafter accelerated H₂O test. These data confirm that theN—N-diglycidyl-4-glycidyloxyaniline stabilized the impregnated towardsliquid water, and it's been directly proven that accelerated water PCR(and OCR) values directly predict the stability of amine sorbents whilebeing exposed to steam. This means that the E3 tri-epoxide speciesstabilized the sorbent at high temperatures in the presence of steam bycovalently cross-linking the amines, which was not shown by thebisphenol A-based epoxy in a previous patent [5].

To give either the amine species or PC₄₀₀ binder of the PEI₈₀₀/E3 BIASpellets resistance to oxidative degradation, K₂CO₃ was added to theimpregnation solution. For this addition, two impregnation solutionswere prepared then mixed together; one solution contained organic MeOH,E3, and PEI₈₀₀ and the other contained inorganic K₂CO₃ and water.Because of the higher heat of vaporization for water than MeOH, thewater content was minimized. In a typical 20 g batch of total bindersolution with K₂CO₃, 17.5 g of MeOH and 2.5 g of water were used. Thiscontrasts 15 g of MeOH and 5 g of water used for an impregnationsolution prepared with a Na₂CO₃ antioxidant, which was not tested due tomore energy needed to evaporate water in the Na₂CO₃ solution. Thishigher energy consumption is a large concern for scale-up of the sorbentto industrial quantities. The combination of (i) K₂CO₃, which requiresless water for solvation and hence less energy for binder solutionevaporation compared to those for Na₂CO₃, with (ii) a 1.5-2.0 mm pelletis an improvement to current state-of-the-art particle technology thatutilized the Na₂CO₃ [5]. FIG. 15 (a) shows that increasing the K₂CO₃content from 0 to 2 wt % (total of dry pellet) enhanced the PCR valuefor pellets oxidatively degraded in air in an oven both at 130° C. for 2hrs and 105° C. for 18 hrs. K₂CO₃ likely served as an oxygen freeradical scavenger, diminishing reactions between oxygen and the aminesites and chloroprene sites. FIG. 4X (b) shows the decomposition of thepellets in air in a TGA set-up while heating from 50° C. at 5° C. min.Results showed that increasing the wt % of K₂CO₃ enhanced thetemperature associated with the maximum degradation/oxidation rate ofthe sorbent, from 164.1° C. at 0 wt % K₂CO₃ to 177.5° C. at 2 wt %K₂CO₃. This indicates chemical interactions between the antioxidant andthe amines, which inhibits amine oxidation in air. The optimum K₂CO₃content of the pellet was 2 wt %, where the pellet still exhibited afresh CO₂ capture capacity of ˜1.6 mmol/g.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention and it is not intended to be exhaustive or limit the inventionto the precise form disclosed. Numerous modifications and alternativearrangements may be devised by those skilled in the art in light of theabove teachings without departing from the spirit and scope of thepresent invention. It is intended that the scope of the invention bedefined by the claims appended hereto.

In addition, the previously described versions of the present inventionhave many advantages, including but not limited to those describedabove. However, the invention does not require that all advantages andaspects be incorporated into every embodiment of the present invention.

All publications and patent documents cited in this application areincorporated by reference in their entirety for all purposes to the sameextent as if each individual publication or patent document were soindividually denoted.

We claim:
 1. A pelletized sorbent for separation of CO₂ from a gaseous mixture, said pelletized sorbent comprising: a first component comprising a Basic Immobilized Amine Sorbent; a second component comprising an inorganic strength additive; and a third component comprising a polymer binder wherein the polymer binder is poly(vinyl chloride), poly(chloroprene), or poly(chloroprene) latex, and wherein the Basic Immobilized Amine Sorbent and inorganic strength additive are interconnected by the polymer binder.
 2. A pelletized sorbent for separation of CO₂ from a gaseous mixture, said pelletized sorbent comprising: a first component comprising a Basic Immobilized Amine Sorbent wherein the Basic Immobilized Amine Sorbent comprises an epoxy-based crosslinker; a second component comprising an inorganic strength additive; and a third component comprising a polymer binder, wherein the Basic Immobilized Amine Sorbent and inorganic strength additive are interconnected by the polymer binder.
 3. A pelletized sorbent for separation of CO₂ from a gaseous mixture, said pelletized sorbent comprising: a first component comprising a Basic Immobilized Amine Sorbent wherein the Basic Immobilized Amine Sorbent comprises an antioxidant; a second component comprising an inorganic strength additive; and a third component comprising a polymer binder, wherein the Basic Immobilized Amine Sorbent and inorganic strength additive are interconnected by the polymer binder.
 4. The pelletized sorbent of claim 3 wherein the antioxidant is an inorganic antioxidant.
 5. A pelletized sorbent for separation of CO₂ from a gas mixture, said pelletized sorbent comprising: a first component comprising a Basic Immobilized Amine Sorbent (BIAS), wherein the Basic Immobilized Amine Sorbent is a Class 1, Class 2, or hybrid Class 1/Class 2 BIAS, and wherein the Basic Immobilized Amine Sorbent is present in the range from about 68% to about 85% of the total dry pelletized sorbent weight; a second component comprising an inorganic strength additive, wherein the inorganic strength additive is fly ash, wherein the inorganic strength additive is present in the range from about 5% to about 37% of the total dry pelletized sorbent weight; a third component comprising a polymer binder wherein the polymer binder is poly(chloroprene) latex and wherein the Basic Immobilized Amine Sorbent and the inorganic strength additive are interconnected by the polymer binder and; a CO₂ sorbent capacity greater than 1.7 mmol/g; a crush strength equal to or greater than 1.0 MPa or attrition value less than 1% after 24 hrs; and a PCR value greater than 50%.
 6. A pelletized sorbent for separation of CO₂ from a gas mixture, said pelletized sorbent comprising: a first component comprising a Basic Immobilized Amine Sorbent, wherein the Basic Immobilized Amine Sorbent is a Class 1, Class 2, or hybrid Class 1/Class 2 BIAS, wherein the BIAS comprises an antioxidant, and wherein the Basic Immobilized Amine Sorbent is present in the range from about 68% to about 85% of the total dry pelletized sorbent weight; a second component comprising inorganic strength additive, wherein the inorganic strength additive is fly ash, wherein the inorganic strength additive is present in the range from about 5% to about 37% of the total dry pelletized sorbent weight; a third component comprising a polymer binder, wherein the Basic Immobilized Amine Sorbent and the inorganic strength additive are interconnected by the polymer binder; a fourth component comprising an epoxy-based crosslinker, a CO₂ sorbent capacity greater than 1.7 mmol/g; a crush strength equal to or greater than 1.0 MPa or attrition value less than 1% after 24 hrs; and a PCR value greater than 50%.
 7. A pelletized sorbent for separation of CO₂ from a gas mixture, said pelletized sorbent comprising: a first component comprising a Basic Immobilized Amine Sorbent (BIAS), wherein the Basic Immobilized Amine Sorbent comprises an epoxy-based cross-linker, wherein the Basic Immobilized Amine Sorbent is a Class 1, Class 2, or hybrid Class 1/Class 2 BIAS, and wherein the Basic Immobilized Amine Sorbent is present in the range from about 68% to about 85% of the total dry pelletized sorbent weight; a second component comprising inorganic strength additive, wherein the inorganic strength additive is fly ash, wherein the inorganic strength additive is present in the range from about 5% to about 37% of the total dry pelletized sorbent weight; a third component comprising a polymer binder, wherein the Basic Immobilized Amine Sorbent and the inorganic strength additive are interconnected by the polymer binder; a CO₂ sorbent capacity greater than 1.7 mmol/g; a crush strength equal to or greater than 1.0 MPa or attrition value less than 1% after 24 hrs; and a PCR value greater than 50%. 